The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is moved by several turbojet engines each housed in a nacelle also housing a set of related actuating devices connected to its operation and performing various functions, when the turbojet engine is operating or stopped.
The nacelle generally has a tubular structure comprising an air intake in front of the turbojet engine, a middle section designed to surround a fan of the turbojet engine, and a rear section designed to surround the combustion chamber of the turbojet engine and able to house thrust reverser means.
Modern nacelles are often designed to house a dual flow turbojet engine capable of generating, by means of the rotating fan blades of the compressor, a hot air flow (also called primary flow) coming from the combustion chamber of the turbojet engine and turbine. The assembly of the compressor, combustion chamber and turbine constitutes a gas generator of the turbojet engine, also called the core.
Thus, a nacelle generally comprises an outer structure, which defines, with a concentric inner structure of the rear section called the Inner Fixed Structure (IFS) surrounding the core of the turbojet engine behind the fan, an annular flow channel, also called a secondary tunnel, aiming to channel a cold air flow, called secondary flow, that circulates outside the turbojet engine.
The rear structure of the core of the turbojet engine ends with a so-called primary jet nozzle ensuring the discharge of the hot air flow, the outer structure of the nacelle generally ending with a secondary jet nozzle, which may have a variable section and optimizing the discharge of the cold secondary flow.
The inner structure thus constitutes a cowling around the core of the turbojet engine and may be referred to using different names, in particular Aft Core Cowl (ACC).
The core cowl and the primary jet nozzle are two separate structures that may in particular move relative to one another, for example due to longitudinal expansion phenomena, variations in flight conditions, or the geometry of the assembly. Transverse movements also exist between the core cowl and attachment pylon of the nacelle.
The structures may also in certain cases be separable from one another for maintenance purposes. The core cowl may in particular be able to be disassembled and removed, so as to allow an access to the core of the turbojet engine. One of the disassembly/movement solutions of the core cowl in particular involves rear translation of the assembly. The primary jet nozzle may also be able to be disassembled so as for example to facilitate its replacement if necessary.
The rear of the turbojet engine is also generally attached to the pylon at the rear attachment point and the interface with the primary jet nozzle may also be produced at the area of that rear attachment point. The primary jet nozzle/pylon interface therefore constitutes an interface zone which, although having a slightly different behavior, in particular due to the fact that the relative longitudinal movements vary, is also affected by the aforementioned problems.
A seal is therefore provided between said aft core cowl and the primary jet nozzle, and/or between the pylon and the primary jet nozzle, said seal being deformable so as to account for the primarily longitudinal and transverse relative movement phenomena to a lesser extent.
Furthermore, the certification constraints for propulsion assemblies require fire protection in an upper 90° quadrant, i.e., 45° on either side of a substantially vertical axis, between the engine core compartment and the outside of the nacelle.
This seal must therefore also provide fire protection between the engine core cowl, the primary jet nozzle and the pylon, so as to avoid the spread of the fire toward or from the engine.
The seals currently used at such interfaces are generally seals of the finger seal type made up of a double row of thin metal strips fixed either to the primary jet nozzle or to the engine core cowl and rubbing on a bearing surface of the opposite part (the core cowl or the primary jet nozzle, respectively).
Examples of such seals are described in particular in document U.S. Pat. No. 5,910,094.
Of course, due to the aforementioned relative movements, these blades undergo friction and in particular a metal/metal contact that leads to significant and often premature wear of the seals.
Known in the state of the art is a solution based on the use of a deformable P seal or Ω seal with a more or less circular section, fixed to one of the parts and bearing or rubbing on the opposite component. Such a seal is described in document WO2006000781 using the term Z seal.
The mounting principle of such a seal and the related flight conditions often mean that, to operate in a normal crushing range known by those skilled in the art, it must have large dimensions, and in particular a large diameter. These dimensions then make it heavy, difficult to install and subject to significant deformation and wear that may lead to damage thereof and thereby compromise its mission as a fire protection barrier.